Ab initio Lattice Dynamics and Grüneisen Parameters of TlGaSe2

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The first-principles calculations of the lattice dynamics of the TlGaSe2 ternary semiconductor compound are presented in this paper. Calculations were performed using open-source code ABINIT on the basis of the density functional perturbation theory within the plane-wave pseudopotential approach. Results on the frequencies of phonon modes in the centre of Brillouin zone and the dispersion of transverse shear acoustic branch of the phonon spectra agree well with experimental data on Raman scattering, infrared reflectivity and ultrasound wave propagation in TlGaSe2. The calculated and experimental temperature dependencies of heat capacity are in a good agreement up to the room temperature. Along the layer, the low-frequency acoustic branch displays the bending wave behavior which is characteristic of the layer crystal structures. We have calculated also the elastic compliances tensor, the directional Grüneisen functions and the coefficients of the linear thermal expansion for TlGaSe2. We obtained that both principal components of the coefficients of linear expansion are positive in the range of temperature above 5 K.
2011-05-25